system/qemu
system/qemu
1
0
Fork 0
mirror of https://gitlab.com/qemu-project/qemu synced 2024-11-05 20:35:44 +00:00
Code Issues Projects Releases Packages Wiki Activity

block/gluster: glfs_lseek() workaround

Browse source 
On current released versions of glusterfs, glfs_lseek() will sometimes
return invalid values for SEEK_DATA or SEEK_HOLE.  For SEEK_DATA and
SEEK_HOLE, the returned value should be >= the passed offset, or < 0 in
the case of error:

LSEEK(2):

    off_t lseek(int fd, off_t offset, int whence);

    [...]

    SEEK_HOLE
              Adjust  the file offset to the next hole in the file greater
              than or equal to offset.  If offset points into the middle of
              a hole, then the file offset is set to offset.  If there is no
              hole past offset, then the file offset is adjusted to the end
              of the file (i.e., there is  an implicit hole at the end of
              any file).

    [...]

    RETURN VALUE
              Upon  successful  completion,  lseek()  returns  the resulting
              offset location as measured in bytes from the beginning of the
              file.  On error, the value (off_t) -1 is returned and errno is
              set to indicate the error

However, occasionally glfs_lseek() for SEEK_HOLE/DATA will return a
value less than the passed offset, yet greater than zero.

For instance, here are example values observed from this call:

    offs = glfs_lseek(s->fd, start, SEEK_HOLE);
    if (offs < 0) {
        return -errno;          /* D1 and (H3 or H4) */
    }

start == 7608336384
offs == 7607877632

This causes QEMU to abort on the assert test.  When this value is
returned, errno is also 0.

This is a reported and known bug to glusterfs:
https://bugzilla.redhat.com/show_bug.cgi?id=1425293

Although this is being fixed in gluster, we still should work around it
in QEMU, given that multiple released versions of gluster behave this
way.

This patch treats the return case of (offs < start) the same as if an
error value other than ENXIO is returned; we will assume we learned
nothing, and there are no holes in the file.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Message-id: 87c0140e9407c08f6e74b04131b610f2e27c014c.1495560397.git.jcody@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>
This commit is contained in:
Jeff Cody 2017-05-23 13:27:50 -04:00
parent eb05e011e2
commit 223a23c198
1 changed files with 16 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

18
block/gluster.c
View file

@ -1275,7 +1275,14 @@ static int find_allocation(BlockDriverState *bs, off_t start,
if (offs < 0) {
return -errno; /* D3 or D4 */
}
assert(offs >= start);
if (offs < start) {
/* This is not a valid return by lseek(). We are safe to just return
* -EIO in this case, and we'll treat it like D4. Unfortunately some
* versions of gluster server will return offs < start, so an assert
* here will unnecessarily abort QEMU. */
return -EIO;
}
if (offs > start) {
/* D2: in hole, next data at offs */
@ -1307,7 +1314,14 @@ static int find_allocation(BlockDriverState *bs, off_t start,
if (offs < 0) {
return -errno; /* D1 and (H3 or H4) */
}
assert(offs >= start);
if (offs < start) {
/* This is not a valid return by lseek(). We are safe to just return
* -EIO in this case, and we'll treat it like H4. Unfortunately some
* versions of gluster server will return offs < start, so an assert
* here will unnecessarily abort QEMU. */
return -EIO;
}
if (offs > start) {
/*